The present invention is particularly applicable to an absorption refrigeration fluid system. The essentials of such a system are shown in FIG. 1 (although heat exchangers are omitted for the sake of clarity). In a typical system like that of FIG. 1, a refrigerant, e.g., water or other phase change substance, is dissolved in an absorbent, e.g., lithium bromide or some other salt. The two materials are often called a "solution pair". The refrigerant is absorbed or desorbed in or out of solution with the absorbent to varying degrees throughout the system, and the heat of absorption is added or extracted to produce heating or cooling effects. Another common solution pair used in an absorption refrigeration system is ammonia as the refrigerant and water as the absorbent.
With reference to FIG. 1, the solution enters the desorber 12 (sometimes called a generator). Heat, Q1, is added to desorber 12. Refrigerant boils off as a vapor leaving what is termed a weak solution. The weak solution returns to absorber 14 via lines 16 and 18 through valve 20. The vapor refrigerant flows via line 22 to condenser 24. External ambient cooling condenses the refrigerant vapor to a liquid, giving off heat, Q2. The liquid refrigerant flows via lines 26 and 28 through valve 30 to evaporator 32. In a refrigeration system, the heat, Q3, gained in the evaporator is from the cooling load. The vaporized refrigerant flows from evaporator 32 via line 34 to absorber 14. The vapor refrigerant is mixed with weak solution in absorber 14, giving off heat, Q4, to create strong solution which is then pumped at pump 36 through lines 38 and 40 from absorber 14 to desorber 12 so that the cycle may continue. Although not shown, system 10 ordinarily includes a first heat exchanger of some type to include lines 40 and 16 and a second heat exchanger to include lines 26 and 34.
The strong solution in an absorption refrigeration system is a liquid and, consequently, is more easily pumped and pressurized than a vapor. Nevertheless, mechanical energy is added to the system at pump 36. After the refrigerant is vaporized with externally added heat and separate from the strong solution, the refrigerant is liquified and reduced in pressure so that, as indicated, at the evaporator, heat may be readily and beneficially absorbed. Thus, valve 30 functions to controllably reduce the pressure of the liquid refrigerant from condenser 24. Typically, the refrigerant is saturated or nearly saturated at that time so that when it passes through valve 30, some of it changes phase and is vaporized. To the degree pressure is reduced and a phase change takes place, energy is lost. Additionally, the weak solution from desorber 12 is depressurized to mix with the depressurized refrigerant in absorber 14. Consequently, energy is again lost at valve 20. Thus, although an absorption refrigeration system is widely used, the conventional system requires a significant amount of energy and, once used, rejects it without reusing or recovering it. The strong solution is pressurized so that the heat rejection portion of the thermodynamic cycle of the refrigerant may take place at a temperature and pressure level which allows the subsequent heat absorption portion of the cycle to take place at a useful level relative to the heat sink, i.e., the environment to be beneficially cooled.
U.S. Pat. No. 1,866,825 shows an expansion engine in the form of helical gears for expanding vapor leaving a desorber and also expanding weak solution leaving the desorber to reduce the heat and high pressure of each fluid and recover the energy thereby to help drive a pump for the strong solution. Smith understood the loss of energy in usual absorption refrigeration systems and presented a device intended to recover some of that energy. The device of Smith, however, was apparently never successful. In any case, a helical gear-type engine is complex and undoubtedly excessively expensive in a modern economy.
U.S. Pat. No. 4,646,541 indicates that various types of motors could be used to reduce pressure in the weak solution and liquid refrigerant streams of an absorption refrigeration system to recover some energy and reduce the requirement of external power for the pump. An expansion, rotary-turbine type engine is disclosed. Although not as complicated as a helical gear engine, a turbine type engine does not provide positive fluid control and presents sealing and other engineering challenges.
Thus, the art does not teach piston devices for recovering the energy in an absorption refrigeration system. In this regard, however, although not a piston device, U.S. Pat. No. 3,791,768 shows a dual chamber diaphragm fluid pump wherein energy from one stream could be used to pump energy in another stream.
As a consequence, the present invention is directed to recovering energy with piston devices from locations in fluid circuits where valves are now commonly used to provide a controlled depressurization.